Hitherto it was usual for belt tensioners to be secured to a vehicle or vehicle seat by screw fasteners, a screw extending through a strap welded to the wall of a tube defining the cylinder. In addition to this, belt tensioners also exist in which an additional element secured to the tube, such as e.g. a cable deflector, is provided with flanges by means of which the belt tensioner can be secured to the vehicle or vehicle seat, the belt tensioner being securely located in at least one plane due to the flat flange. However, providing straps or flanges welded to a tube or to an additional element for securing the belt tensioner makes its manufacture more expensive.